Enhanced Trypanosoma musculi infections in mice with concomitant malaria

Concomitant infections, parasites and immune responses

Concomitant infections are common in nature and often involve parasites. A number of examples of the interactions between protozoa and viruses, protozoa and bacteria, protozoa and other protozoa, protozoa and helminths, helminths and viruses, helminths and bacteria, and helminths and other helminths are described. In mixed infections the burden of one or both the infectious agents may be increased, one or both may be suppressed or one may be increased and the other suppressed. It is now possible to explain many of these interactions in terms of the effects parasites have on the immune system, particularly parasite-induced immunodepression, and the effects of cytokines controlling polarization to the Th1 or Th2 arms of the immune response. In addition, parasites may be affected, directly or indirectly, by cytokines and other immune effector molecules and parasites may themselves produce factors that affect the cells of the immune system. Parasites are, therefore, affected when they themselves, or other organisms, interact with the immune response and, in particular, the cytokine network. The importance of such interactions is discussed in relation to clinical disease and the development and use of vaccines.

Acquisition of resistance to the tick Amblyomma variegatum in Boran cattle, Bos indicus and the effects of Trypanosoma congolense and Babesia bigemina on host resistance

Resistance was induced in cattle to the tick Amblyomma variegatum by five consecutive infestations with nymphs and adults. Using the principal component analysis (PCA), it was found that percentage of adults engorged, percentage of adults which died, percentage of nymphs which engorged, percentage of nymphs which moulted and percentage of nymphs which died, were the main indicators of resistance against A. variegatum. The percentages of nymphs which engorged or moulted after the third infestation were significantly (P < 0.01) reduced while the percentage of nymphs which died increased significantly (P < 0.01) after the third infestation. Percentages of adults which engorged or died started to decrease significantly (P < 0.01) from the fourth infestation after an initial increase during this period. The acquisition of resistance by cattle to the adult ticks was slower than to the nymphs. Infection of cattle with Trypanosoma congolense and Babesia bigemina after the fifth infestation enhanced the acquired immunity as revealed by the significantly (P < 0.01) increased feeding period of the adult ticks and changes in other parameters.

Cell mediated immunity in childhood malaria

Children with malarial infection, due to P. Vivax and P. falciparum, were tested for cell mediated immunity (CMI) by lymphocyte proliferative response to mitogens PHA (phytohaemagglutinin) and PWM (poke weed mitogen) and antigen PPD (purified protein derivative). This was done during the period of parasitemia and after treatment, and compared to 19 normal matched controls. There was no significant difference between the patients and the control group with regard to PHA (patients 57.4 +/- 50.5; controls 61.3 +/- 54.9); PWM (patients 27.4 +/- 19.9, controls 29.9 +/- 24.5); PPD (patients 2.2 +/- 1.2, controls 1.9 +/- 1.4). There was also no significant difference in the lymphocyte responses during the period of parasitemia and after treatment. Hence, there does not seem to be any depression of CMI as shown by lymphocyte proliferative responses during childhood malaria.

Specific humoral depression in chronic patients infected by Trypanosoma cruzi

Realizamos um estudo comparativo entre o xenodiagnóstico e os testes sorológicos para a doença de Chagas. Cento e cincoenta pacientes de algumas áreas endêmicas foram estudados. Quatro deles pareceram revelar um estado particular com um xenodiagnóstico positivo e uma sorologia negativa, esta realizada com quatro diferentes técnicas clássicas (teste de immunofluorescência, ELISA: Enzyme Linked Immunosorbent Assay, teste de fixação do complemento e teste de immuno-eletroforese). O soro de um dos pacientes que apresentou depressão humoral específica mostra elevada quantidade de antígenos circulantes comprovada pela técnica da immuno-eletroforese. Os Autores sugerem o uso de um teste sorológico para detectar a presença de antígenos circulantes de T. cruzi, além da utilização de testes sorológicos clássicos. Isto permitiria o diagnóstico da doença de Chagas em pacientes com uma baixa (ou mesmo inexistente) produção de anticorpos específicos.

[Dynamics of splenic lymphocytes and immunosuppression in Toxoplasma infected mice (author's transl)]

Mice infected with high-virulent strains of T. gondii sustained a marked decrease of splenic lymphocytes within 7-10 days after infection, just prior to death. When infected with a low-virulent strain, the numbers of splenic lymphocytes and of T-lymphocytes fluctuated, but gradually increased over a period of 30 days. To evaluate their immunologic potential, the mice infected with a low-virulent strain of Toxoplasma were immunized with sheep erythrocytes on different days after infection, and antibody levels were measured by direct hemagglutination. Antibody response was minimal when sheep cells had been injected 10 days after infection with Toxoplasma; subsequently immunologic reactivity improved, but even after 30 days anti-sheep agglutinin titers were still below pre-infection levels.

Exacerbation of experimental Trypanosoma cruzi infection in mice by concomitant malaria

The effect of malaria on the chronic phase of Chagas' disease was investigated in mice. The animals were given Plasmodium bergheri-infected red blood cells 2 to 12 months after their initial inoculation with trypomastigotes of 3 different strains of Trypanosoma cruzi (Y. CL and Gilmar). in all the experiments carried out with one of the strains (CL), a somewhat variable but always considerable percentage of mice (average 39%) relapsed in to the acute phase of Chagas' disease. This relapse was characterized by a significant increase in the number of circulating trypomastigotes. Recrudescence was observed also with a 2nd strain of T. cruzi (Gilmar), which is similar in many aspects to the CL strain, e.g. the morphology of blood stages, curved of parasitemia and susceptibility to antibodies in vitro. In mice whose chronic phase was induced by trypomastigotes of the Y strain, malaria infections did not induce a typical acute phas with high parasitemia by T. cruzi. Bloodstream forms of Y parasites differ from those of CL and Gilmar strains morphologically as well as immunologically, i.e. only the Y strain is easily agglutinated and partly inactivated by specific immune serum. In light of this and other known characteristics of the strains used in the present work, the author speculates on mechanisms which allow malaria infections selectively to suppress acquired host resistance to certain strains of T. cruzi.